1. Field of the Invention
This invention pertains to new catalysts for promoting the reaction between organic isocyanates and organic compounds bearing active hydrogen (i.e., active in the Zerewitinoff test). The new catalysts are particularly useful in promoting the reaction of organic isocyanates with aliphatic hydroxyl compounds to produce urethanes.
2. Description of the Prior Art
Reactions of isocyanates with compounds bearing active hydrogen are well known. This type of reaction is used, for example, to produce urethanes (i.e. carbamates), ureas, etc. Commercially, the most important reaction is in the production of polyurethanes by the reaction of ployisocyanates with aliphatic polyols.
Various catalysts have been used in promoting the the urethane reaction, but the most common commercial catalyst is 1,4-diazabicyclo[2.2.2]octane. This particular compound as well as certain other tertiary amines are very effective. Indeed, 1,4-diazabicyclo[2.2.2]octane is so effective that the "pot life" of the reaction mixture is very short and this presents a processing problem in commercial applications (such as carpet foam-backing, etc.) which require that the reaction mixture be doctorable for a period of time.
Erner et al. described a class of imidazole catalysts in U.S. Pat. No. 3,152,094 that was said to be unreactive in the mixture of urethane reactants at ambient temperatures but highly effective catalysts at moderately elevated temperatures (e.g. about 75.degree. C.). These catalysts were represented by the formula ##STR2## wherein R.sub.2 is hydrogen, alkyl or benzyl; R.sub.1 and R.sub.3 are hydrogen, alkyl, benzyl, or joined to form a 6-membered carbocyclic ring, provided that the total number of carbon atoms in the substituents R.sub.1, R.sub.2 and R.sub.3 does not exceed 12. The disclosure of Erner et al. (U.S. Pat. No. 3,152,094) is hereby incorporated by reference.